Corby shows how a Lib Dem collapse will hurt the Tories

A fall in support for the Lib Dems will propel Labour to victory in Tory marginals.

The Liberal Democrats lost their deposit in the Corby by-election after finishing fourth behind Ukip. Photograph: Getty Images.

One the most notable things about the result of the Corby by-election is the collapse of the Lib Dem vote. The party saw its share of the vote fall from 14.5 per cent to just 5 per cent as it was pushed into fourth place by Ukip, which won nearly three times as many votes (5,108 to 1,770).

Many of those who voted for the Lib Dems in 2010 will have defected to Labour, which saw its vote increase by 9.8% to 48.4%, propelling the party to victory against the Conservatives. If this patten is repeated at the general election, the Tories stand to lose dozens of seats - there are 37 Conservative-Labour marginals where the third place Lib Dem vote is more than twice the margin of victory. Even if Nick Clegg's party partially recovers before 2015, Labour will make sweeping gains. In addition, while existing Lib Dem MPs, many of whom enjoy large local followings, are likely to benefit from an incumbency effect, it is the Tories, not Labour, who will suffer as a result - David Cameron's party is in second place in 38 of the Lib Dems' 57 seats.

If they are to stand any chance of winning a majority at the next election or even remaining the largest single party, the Tories need to hope for a Lib Dem recovery.